I suggest you ...

Better Theme / Styling support

As the feedback to the VS11 beta screenshots demonstrated, many developers are passionate about the feel of the IDE they use. It is probably a given that no one style will make everybody happy.

However, there's a solution - allow loadable, shareable themes. While VS2010 has this to some extent with the theme editor addin, there are many aspects of the UI that are not stylable.

The UI for VisualStudio should support alterations to all visual aspects through some method. While support for theme creating, editing, importing, and exporting would be appreciated, full themability exposed via an API would allow this niche to be filled via an addin.

Note that any aspect of the UI that can not be recolored or redrawn via a theme will detract from the usefullness of styling (for example, the text editor window scrollbars in visual studio 2010)